This chapter provides an overview of aortic valve replacement (AVR) with stented bioprostheses. The indications for aortic valve surgery are reviewed with an emphasis on evidence-based guidelines and contemporary clinical and physiologic outcomes of aortic valve surgery with currently available stented bioprostheses.
NATURAL HISTORY AND INDICATIONS FOR OPERATION
Aortic stenosis (AS) is primarily caused by degenerative calcification in patients over 70 years of age and bicuspid aortic valve in patients under 70 years of age in the developed world. Rheumatic valve disease is the third most common cause of AS affecting patients across the age spectrum. AS is also associated with systemic diseases such as Paget’s disease of bone and end-stage renal disease. The pathogenetic mechanisms of aortic valve calcification include valvular interstitial cell transformation, inflammation and lipid accumulation, reminiscent of the pathogenesis of atherosclerotic plaques.1 The overall incidence of calcific AS is rising with the aging population in developed countries. A population-based study of Olmstead County reported the increase in prevalence of degenerative AS and other valvulopathy in patients with age from 55 to 64 (0.6%), 65 to 74 (1.4%) and ≥75 years (4.6%; p < .0001, Fig. 28-1).2
Prevalence of valvular heart disease by age (A) Frequency in population-based studies (N = 11,911) and (B) in the Olmsted County community (N = 16,501). (Reproduced with permission from Nkomo VT, Gardin JM, Skelton TN, et al: Burden of valvular heart diseases: a population-based study, Lancet 2006 Sep 16;368(9540):1005-1011.)
Valvular degenerative calcification is characterized as a progressive reduction of orifice cross-sectional area caused by calcification of the cusps. The normal human aortic valve area (AVA) is between 3.0 and 4.0 cm2 with minimal to no gradient. AS is defined as mild, moderate, severe and very severe with the corresponding AVA, mean gradients and peak jet velocities as shown (Table 28-1). In the presence of normal cardiac output, transvalvular gradient is usually greater than 50 mm Hg when the AVA is less than 1.0 cm2.3 A rapid increase in transvalvular gradient is seen with AVAs between 0.7 and 1.0 cm2. However, discordant echocardiographic parameters are not uncommon. Minners et al4 examined 3483 echocardiographic studies with severe AVA, 25% had less-than-severe mean gradient and 30% has less-than-severe peak velocities leaving only 40% of patients with all echocardiographic criteria consistent with severe AS. Thus, echocardiographic data require careful assessment of images and correlation with hemodynamic parameters such as preload and afterload conditions.
TABLE 28-1:Classification of AS